A gas turbine engine designed for use in aircraft typically includes one or more units, such as gearboxes, supplied with lubricant by a positive displacement pump directly driven by the compressor section of the engine. As the aircraft ascends from sea level to altitude, the power output of the engine decreases thereby reducing the amount of lubricant needed by its associated units to maintain satisfactory operation. However, the rotational speed of the engine and, hence, the speed of the lubricating pump are held relatively constant. As a result, the flow of lubricant to the units also remains relatively constant at a rate in excess of their requirements under reduced power conditions. Moving parts, such as gears within the units, churn the excess lubricant and consume energy needlessly thereby reducing the efficiency of the engine. To eliminate this problem, the present invention provides control means for reducing the flow of lubricant to the units when the engine operates at altitude, thereby improving engine efficiency. Fail safe protection is also provided to assure an adequate supply of lubricant to the units in the event that the lubricant control means should malfunction.